1. Field of the Invention
The present invention relates to the field of cell isolation. The present invention also relates to methods isolating various types of stem cells or progenitor cells.
2. General Background and State of the Art
Bone marrow is known to contain hematopoietic and mesenchymal stem and progenitor cells. Hematopoietic stem cells (HSCs) can generate various types of blood cells [1], and marrow stromal cells (MSCs) or mesenchymal stem cells are capable of differentiating into several different tissues including cartilage, bone and adipose [2,3,4]. MSCs were first found by Friedenstein and his colleagues [5] based on their adherence to cell culture dish. Undifferentiated MSC are fibroblast-like in morphology, self-renewable, and capable of differentiating into mainly connective tissues of the mesoderm origin, namely cartilage, bone, and fat. There are no certain cell surface proteins that specifically and uniquely identify MSCs yet. The diversity of characteristics associated with MSC can be explained by differences in tissue origin, isolation methods and culture conditions between laboratories [2,6,7,8]. Although there is no consistency, MSCs expanded in vitro express CD29, CD44, CD73, CD105, CD106, and CD166 [9], but lacks or are dimly positive for hematopoietic surface markers, such as CD11b, CD14, CD31, CD34, or CD45.
Cell populations with characteristics similar to MSC from different sources including mainly bone marrow, umbilical cord blood, and fatty tissue are known. Although it is difficult to identify whether these cells are distinct cell types due to lack of characteristic markers, they have some different level of surface marker expressions and various differentiation abilities, probably due to their distinct isolation and culture methods. The range of differentiation potential of MSCs is expanding, not only to mesoderm lineages but also to endoderm and/or ectoderm lineages. Therefore, the term “multi-lineage stem or progenitor cell (MLS/PC)” is suggested for these types of stem or progenitor cells capable of differentiating to mesoderm, ectoderm and/or endoderm lineages.
MSCs derived from adult bone marrow offer the potential to open a new strategy in medicine due to its ease of isolation and culture, stability of their phenotype in vitro and low or no allogeneic rejection. In fact, experimental evidence of the hypo-immunogenic nature of MSCs in humans and animals has been accumulating [10]. Currently, clinical applications of adult autologous or allogeneic MSCs have been conducted to treat a variety of diseases, and have generated very promising results [11].
Several protocols have been developed for isolation and expansion of MSCs in culture so far. These methods are based on using density-gradient centrifugation [12], FACs sorting [13,14], specific cell surface antibody [12,15,17,18], selective adhesion to laminin-coated plate [19], Hoechest dye exclusion, and size-sieved culture [24]. Potential disadvantages of these methods in terms of clinical applications are the heterogeneity of cultured cells, high risk of contamination, and/or high cost of production. Therefore, a new protocol to isolate highly homogeneous cell populations with less contamination potential and cost is desired for use in clinical settings.
The present application discloses a new isolation method developed to produce a highly homogeneous population of MLSCs with less contamination potential and cost for clinical applications. This method does not necessarily utilize density-gradient centrifugation, antibody selection, or FACS sorting, but preferably uses mainly natural gravity in a non-coated, collagen or polylysine-coated culture dishes and subfractionation cell culture to separate adherent bone marrow cells according to their cell density. Several distinct highly homogeneous populations of MLSC lines derived from single-cell derived colonies were isolated and expanded with this protocol from human bone marrow. These stem cell lines are self-renewable and capable of differentiating into several different lineages, such as chondrogenic, osteogenic, adipogenic, neurogenic, and hepatogenic lineages.